Means and method of damping pitcing and rolling of floating structures under wave and swell action



March 5, 1968 L. J. TSOKALAS 3,

MEANS AND METHOD OF DAMP PITCHING AND ROLLING OF FLOATING STRUCTURES ER WAVE AND SWELL ACTION Filed Oct. 6, 1966 5 Sheets-Sheet 1 INVENTOR Y M33 y ATTORNE s March 5, 1968 .J. TSOKALAS 3,371,640

MEANS AND METHOD DAM G PITCHING AND ROLLING 0F FLOATING STR URES UNDER WAVE AND SWELL ACTION Filed Oct. 6, 1966 5 Sheets-Sheet 2 META CENTER CENTER OF PRESSURE (VENT OPEN) CENTER OF PRESSURE FIRST STAGE 9 HINGED VENT COVERS 5: 5; Y 5 4 SECOND STAGE INVENTOR VENT v DlflliTlON: 5 F2 I {3v M g WAVES -D CENTER OF PRESSURE E I 6 SECOND STAGE Aficfif vw 3,371,640 MEANS AND METHOD OF DAMPING PITCHING AND ROLLING OF FLOATING March 5, 1968 L. J. TSOKALAS STRUCTURES UNDER WAVE AND SWELL ACTION u Filed Oct. 6, 1966 5 Sheets-Sheet 5 7 INVENTOR Mfim ATTQRNEYZ,

March 5, 1968 J. TSOKALAS 3,371,640

MEANS AND METHOD OF DAMPING PITCHING AND ROLLING OF FLOATING STRUCTURES UNDER WAVE AND SWELL ACTION Filed 001, 6, 1966 5 Sheets-Sheet 4 12 CENTER or cmw/rv vavr 0P6) 12a 12 CENTE'R 0F cR v/rv 5 I I 1 vewr open) 7 V I 45 15 (5/170? or mcssuns (vewr om) (ENTER 0F PRESSUR (vewr OPE/l) 3,371,640 FLOATING March 5, 1968 .1. TSOKALAS MEANS AND METHOD OF DAMPING PITCHING AND ROLLING OF STRUCTURES UNDER WAVE AND SWELL ACTION 5 Sheets-Sheet 5 Filed Oct. 6, 1966 INVENTOR. a% -W- BY United States Patent 3,371,640 MEANS AND METHOD OF DAMPING PITCHING AND ROLLING 0F FLOATING STRUCTURES UNDER WAVE AND SWELL ACTION Leo J. Tsokalas, 20 Gardner St., Manchester, Conn. 06040 Filed Oct. 6, 1966, Ser. No. 600,295 13 Claims. (Cl. 114-121) riding a wave or swell, from what it would be with normal water displacement of the structure without this means, to thus reduce the pitch or roll of the structure which would otherwise occur.

It is another object to provide a structure whereby damping of its pitch or roll, under action of waves or swells, is elfected by one or more vents in the form of longitudinal passages located either fore or aft of the center of gravity of the structure and arranged to allow water, as in waves or swells having a surface level higher than the normal static water level, to enter or pass through to thus decrease both the buoyant elfect or force and moment arm about the center of gravity, below what they would be with the normal structure without these vents.

It is a further object to provide a means of damping pitch orroll of a floating structure under wave or swell action, which will cancel out or reduce the buoyancy effect of a volume of water proportional to the wave length and frequency.

With the foregoing and other objects in view, I have devised the novel method with means by which it may be accomplished as illustrated in the accompanying drawings forming a part of this specification. It is, however, to be understood the invention is not limited to the specific details shown or described, but may embody various changes and modifications within the scope of the invention.

In these drawings:

FIG. 1 is a plan view showing diagrammatically a torus type of body or floating structure illustrating one form and application of my invention;

FIG. 2 is a transverse section thereof substantially on line 22 of FIG. 1 and showing it in a position of rest on a normal static water level;

FIG. 3 is a section substantially on line 3-3 of FIG. 1 showing the device in a tipped position from that of FIG. 2 under wave or swell action;

FIG. 4 is a partial edge view taken substantially on line 44 of FIG. 1;

FIG. 5 is a diagrammatical section of the structure showing it in a tipped position under wave or swell action, and indicating some of the forces involved;

FIG. 6 is a similar section showing it tipped in the opposite direction;

FIG. 7 is a diagrammatical section showing a somewhat modified arrangement of the damping means, the structure being shown in a position of rest on a normal static water level;

FIG. 8 is a similar diagrammatic section to FIG. 7, showing the structure tipped to a dynamic condition under wave or swell action;

FIG. 9 is a diagrammatic section showing a further somewhat modified arrangement of the damping means, and showing the structure tipped to a dynamic condition under wave action;

3,371,640 Patented Mar. 5, 1968 1212 of FIG. 10;

FIG. 13 is a diagrammatic section similar to FIG. 8, illustrating various dynamic conditions;

FIG. 14 is a partial plan view showing a vent with a rotatable bottom portion;

FIG. 15 is a transverse section taken substantially along the line 1515 of FIG. 14;

FIG. 16 is a top plan view of a tri-maran hull constructed in accordance with my invention;

FIG. 17 is a side elevational view of the tri-maran of FIG. 16;

FIG. 18 is a sectional view taken substantially along line 18-18 of FIG. 17 showing one way my damping means may be applied to a tri-maran hull;

FIG. 19 is a sectional view similar to that of FIG. 18 showing a modified way in which my damping means may be applied to a tri-maran hull;

FIG. 20 is a top plan view of a catamaran hull constructed in accordance with my invention; and

FIG. 21 is a side elevational view of the catamaran of FIG. 18.

In these drawing, FIGS. 1 to 4 are to represent as an example and diagrammatically, a floating platform-suitable for various operations, and of any desired size, capable of sitting on the water in all kinds of weather for extended periods of time. The seaworthy capability is the result of damping eflects of various arrangements of vents, features which will later be described.

Damping is achieved by allowing water into and/or through the vents, thus arresting or controlling the buoyant force and moment of wave or swell action acting on the body for a given time, a function of the size and angle of the vents and wave height and frequency, after which the top inside surface of the vents may provide a second stage buoyancy.

Essentially the vents serve to effect a time lag providing for a more gradual righting force thereby maintaining a bow-up attitude and minimizing pitch and roll while the floating body or structure remains in a giyen area without (or with) benefit of anchor.

Examples of applications of the device are:

Helicopter pods and landing platforms Floating docks Otf-shore missile launchers Off-shore antenna platforms Floating bridge sections Off-shore oil well drilling rigs Life rafts (inflatable) Off-shore desalination platforms Otf-shore oceanographic research platforms Lightships or stations The torus hull form of FIGS. 1 to 4 comprises an outer circular buoyant portion 1 supporting a platform 2. This is used as illustrative of the device, as it will be understood it may be of different shapes as well as of diflerent cross sections. The buoyant section is shown as being solid of buoyant material, but it may be of hollow or pontoon construction, and although shown in one continuous piece, may be made in connected sections. In other words, the device shown is to illustrate the principle and function of the invention without going into the specific constructions which may be used. FIGS. 5 to 9 and 13 are diagrammatic views to illustrate different positions and conditions in use of the device, and the forces or eflects involved in these positions and conditions.

As shown the device is provided with one or more vents 3 in the fore or bow portion 8 and one or more vents 4 in the aft or stern portion 9, the direction of wave or swell motion being from fore to aft as indicated by the arrows 5. These vents are in the form of passages through the buoyant portion into which the water may enter or pass through. The vents 3 in the fore part are preferably inclined as shown, with their front entrances 10 higher than or above the rear 11, and the aft vents may be substantially level or horizontal, as shown in FIGS. 1 to 6, or inclined at different angles as shown in FIGS. 7, 8 and 9. In all cases the vents or passages extend generally longitudinally of the device considered with relation to the fore and aft dimension of the device and the direction of wave and swell motion, although, due to the shape of the device, some of the vents or passages may be somewhat inclined laterally or vertically to this longitudinal designation, as shown. These vents or passages are also located mostly or generally above the static normal water level 6, as shown in FIG. 2, when the device is floating in stationary position on this water level, although the amount will depend on the loading of the device. The center of gravity is indicated at 12 and center of displacement or center of buoyancy (pressure) is shown at 15.

It will be understood as indicated that the angle of inclination and volume or cross sectional area, and also shape of the vents may vary depending on conditions and uses involved. Furthermore, the angle of inclination and volume or cross sectional area and also shape of the vents or passages may be variable by constructing the portion of the body below the vent as a separate notatable member as shown in FIGS. 14 and 15. In FIG. 3 is shown an action and effect secured by a wave or swell, indicated by line 7, moving fore and aft in the direction of the arrows 5. The wave is shown as having passed the fore part of the device, but is just passing the aft part. It will be seen the effect is to raise the aft part to the static position or to maintain its attitude. If the aft part had been solid or full section and minus the vents 4, maximum displacement of the body would have been caused, as maximum buoyancy of the wave would have been imparted to the aft portion. However, with the vents 4, a portion of the wave enters and passes through these vents, imparting less buoyancy to the aft portion than would have been the case with full section of this portion. Similarly, as the wave passed the fore portion a part of the water entered the vents 3, reducing the buoyancy and therefore lift of this portion under what it would have been with full section. The result is much less pitch and roll of the device over what it would have been without the vents.

The action and results secured under various conditions are illustrated in the diagrammatical views of FIGS. 5 to 9 and 13. In these views merely the transverse section of the torus form with supported platform and illustrative vents are shown.

In the arrangement of FIG. 5, a wave indicated by line 7 is passing the aft portion as in FIG. 3. If we assume the center of gravity 12 and center of displacement 15 are on the vertical center line 13, with 15 below 12, as shown in FIG. 2, when the structure is in the static normal position, then as the aft portion is raised by action of the wave the center of displacement, or upward pressure (buoyant force or center of buoyancy) 15, is shifted to the left of the center of gravity. The metacenter 16 at the intersection of vertical line 14 through the pres- :sure center 15 and line 13 is higher than the center of gravity 12. The resulting couple or righting moment M tending to return the structure to the static position of FIG. 2, consists of the forces acting through points 12 and 15 about the distance D, and is indicated by the .curved arrow 17. The device thus has effective tability.

In FIG. 6 the effect of a wave indicated by line 18 passing the fore portion is shown. The reduced buoyancy effected by both vents 3 in the fore portion and 4 in the aft portion is indicated. In the first stage due to the effect and reduction in buoyancy of part of the wave entering or passing through the vents 3, and water entering the aft vents as the aft portion is depressed, the center of displacement or center of buoyancy 15a is displaced to the right of center of gravity 12 by amount d. The metacenter (not shown) at intersection of vertical line 14a with vertical center line 13 is above center of gravity 12, therefore stability is retained and couple or moment M0 indicated by curved arrow 17a, tending to return the structure to the normal or static position of FIG. 2, consists of the forces through 12 and 15a about the ditsance d. In addition to the damping effect just described, there may also be a second stage or effect by impingement of the water on the top surface of the vents. Thus the water impinging on the top surfaces 4a of vents 4 produces a second stage buoyancy. This would tend to decrease the dip of the aft portion and tend to assist in righting the structure and thus reduce the pitch or roll. This effect is indicated by shifting center of displacement or center of buoyancy further to the right of center of gravity 12, as indicated at 15b, and the couple or righting moment tending to return the structure to the static condition consists of forces through 12 and 15b about line D. The effect or amount of damping secured by the vents may be varied and controlled by vent covers 19 with means (not shown) for shifting between open and closed positions and capable of holding them in these or intermediate positions. These covers may be used for any or all of the vents, either fore or aft, as desired or found necessary.

The section of FIG. 7 is similar to that of FIG. 2 with the structure in the normal static condition on normal static water level 6, except the vents 3a in the fore portion are inclined less than the vents 3 in FIG. 2, and the vents 4b in the aft portion are inclined at a greater angle than vents 4. As previously stated, the damping effect is achieved by allowing water into and/ or through the vents, thus arresting or reducing the buoyant force and moment acting on the body for a given time, which is a function of the size and angle of the vents and wave height and frequency.

In FIG. 8 is indicated diagrammatically the effect of a wave, indicated by line 7, on the form of FIG. 7 as it passes the aft portion 9. The shifting of the center of pressure (center of displacement or center of buoyancy) to the left or forward of the center of gravity 12 with the vents open, is indicated at 15c, and with the vents closed, at 15d.

FIG. 13 is similar to FIG. 8 and further illustrates the floating body under varying dynamic conditions. In FIG. 13 the reduction of buoyancy may be seen as an interplay of buoyancy and ballast effecting the shifting of the center of gravity 12 in relation to the shifting of the center of pressure 15 as the wave passes through the vents. The time lag effect, or more gradual righting effect, may be seen as a shifting aft of the center of gravity 12 which effects a smaller moment arm a due to the larger volume of water passing through the aft vents 4b. The effect is to raise the aft part to the static position or to maintain its attitude by a wave passing through the aft vents.

In FIG. 9 is indicated diagrammatically a form similar to FIGS. 1 .to 8, in which fore vents 3 are steeply inclined as in FIGS. 1 to 6, while the vents 4c in the aft portion are more steeply inclined than those of the other figures. The body is also shown as tipped or inclined from the static position by wave 7a passing the aft portion. Thus in the static normal position the volume of buoyancy is equal on all portions. For dynamic condition and wave moving fore and aft, the volume of buoyancy is unequal above the static water line with the forward end or portion having more buoyancy. Tipped angle is indicated by line 6a.

In FIGS. 14 and 15 is illustrated a form of the floating body 1 wherein the vent 4 is defined by an upper portion 26 and a lower portion 27. In this form, the lower portion is rotatably mounted upon the hinge pin 28, thereby allowing the angle of the vent to be changed as shown inthe dot-dash lines of FIG. 15. This variable vent opening or passage permits the stability of a given craft to be maintained through a wider range of sea conditions.

The damping effect described, including the first and second stage buoyancy, as described in connection with FIG. 6, may be obtained on conventional shaped hulls, of ships or vessels. This is shown diagrammatically in FIGS. and 11.

In these views a hull of any size and conventional shape is indicated in outline at 20, the normal static water line being indicated at 21. In the opposite sides of the aft portion, the cross-sectional area, or normal displacement of this portion, is reduced immediately above this normal static water line or level, by longitudinal vents in the form of channels 22 on the opposite sides of the hull running fore and aft at this level. These channels are open at their forward and stern ends 23 and 24. They may extend a proportionate length of the hull as is found necessary for the damping eflect desired. About half the length of the vessel is the normal amount. The damping effect secured by these channels is indicated in FIG. 11, where the top of a wave moving fore and aft in the direction of the arrows 5, is indicated by the line 24. It will be seen that the buoyancy of the wave on the aft portion is reduced by part of the wave passing into and through the channels 22, over what it would be by a full cross section of the hull without these channels, thus reducing the lift of the aft portion and the pitch and roll of the vessel by the wave. Also the second stage buoyancy effect described in connection with FIG. 6, to reduce dip or drop of the aft or stern portion by lifting of the bow or forward portion by a wave, may be secured by impact of the top of the wave on the upper surfaces of the channels. The outer sides of the channels 22 may be covered by covers 25 if desired to maintain the outer normal surface appearance of the hull. The cross-sectional area of these channels is determined by the size of the vessel and amount of damping desired, which is a function of the area of the openings or channels in relation to wave frequency and length. It will be seen from the above that damping is achieved by allowing water from the waves moving fore and aft into and/or through the vents or channels, thus arresting or reducing the buoyant force and moment acting on the body or structure for a given time, a function of the size and angle of the vents and wave height and frequency. Essentially the vents serve to effect a time lag, providing for a more gradual righting force, thereby maintaining a bow-up attitude and minimizing pitch and roll, even while the body or vessel may remain in a given area without benefit of anchor. Damping is secured by decreasing the buoyancy of the body fore or aft of its center of gravity, or both, thereby decreasing the buoyant force acting on the fore or aft portion or end of the body, thus eliminating violent pitch and roll in heavy seas. It is secured by allowing water from the waves to enter into and/or through the vents, depending upon location, size and angle of the vents peculiar to the configuration of the body or structure involved, thus decreasing both the buoyant force and moment arm. After the wave crest goes by, the structure maintains normal buoyancy without quick pitch or roll.

FIGS. 16-19 show how my invention may be utilized in a tri-maran hull form. It should be noted that in this form, the vents 30 are aft of the center of gravity 12 and are transverse to the longitudinal axis of the body 29, be-

ing directed towards the center thereof. The inclinationof the Vents 30 may take the form of either FIG. 18 or FIG. 19 as both configurations will operate to ballast the body 29 and to secure the desired damping effect against rolling movement of the body when a wave passes transversely of the body into and through the vents 30.

FIGS. 20 and 21 show how my invention may be utilized in a similar manner in a catamaran hull form with the transverse vents 32 being formed forward of the center of gravity 12 of the body 31 and transverse vents 33 being formed aft of the center of gravity 12.

The torus hull with vents closed after alighting on the water serves as a suction device affording a safety margin in extreme conditions for the smaller machines (20 feet diameter).

Shallow draft ships and boats having greatly improved power to weight ratios may be realized through use of the above described invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A floating body having volume and weight, displacing water on which it is floating, said body provided with one or more vents each in the form of a straight longitudinal passage open at its opposite ends, both ends of all of said vents being disposed on the external surface of said body above the normal water level and one of said ends of each vent disposed adjacent said water level when the water is calm, each of said vents located so as to extend longitudinally of the body solely in an outward direction away from its center of gravity and adapted to receive and permit passage of a portion of a wave moving from fore to aft and thus reduce the Water displacement and buoyancy of the portion of the body provided with the vent or vents from what they would be with the full volume of the body without the vent or vents.

2. The floatingbody of claim 1 in which the vent or vents are located to extend aft of the center of gravity of the body and are inclined upwardly from fore to aft.

3. The floating body of claim 1 in which the vent or vents are located forwardly of the center of gravity of the body and are inclined downwardly from fore to aft.

4. The floating body of claim 1 in which said vents are located both fore and aft of the center of gravity of the body, said vents being oppositely inclined, the fore ones downwardly from fore to aft.

5. The floating body of claim 1 in which there is a closure for at least one end of a vent movable between open and closed positions.

6. The device according to claim 1 in which the body is of generally torus shape comprising an outer peripheral buoyant structure in which the vent or vents are located.

7. The device according to claim 1 in which the floating body is a ship having an elongated hull, and the vents are channels in the opposite outer sides thereof disposed entirely in the aft portion and extending longitudinally above the normal static water level.

8. A floating body having volume and weight, displacing water on which it is floating, said body provided with one or more vents each in the form of a straight longitudinal passage open at its opposite ends, both ends of all said vents being disposed on the external surface of said body above the normal water level and one of said ends of each vent disposed adjacent said water level when the water is calm, each of said vents arranged to receive and permit passage of a portion of a wave and thus reduce the water displacement and buoyancy of the portion of the body provided with the vent or vents from what they would be with the full volume of the body without the vent or vents.

9. The floating body of claim 8 wherein each end of each of said vents includes a vent cover movable between an open and a closed position.

10. A floating body having volume and weight, displacing water on which it floats, said body provided with one or more vents each in the form of a straight longitudinal passage open at its opposite ends, both ends of all of said vents being disposed on the external surface of said body above the normal water level when the water is calm, each of said vents located so as to extend transversely of the longitudinal centerline of the body and adapted to receive and permit passage of a portion of a wave moving transversely of the body and thus reduce the water displacement and buoyancy of the portion of the body provided with the vent or vents from what they would be with the full volume of the body without the vent or vents.

11. The floating body of claim 10 wherein the vent or vents are located aft of the center of gravity of the body.

12. The floating body of claim 10 wherein the vent or vents are located both forwardly of and aft of the center of gravity of the body.

13. A floating body having volume and weight, displacing water on which it is floating, said body provided with one or more vents each in the form of a passage open at its opposite ends, both ends of all said vents being disposed on the external surface of said body, said vent or vents defined by a top wall portion and a bottom wall portion, said bottom wall portion being rotatably secured to said body so as to enable the angle of the vent or vents to be changed to form a variable vent opening or passage, adapted to receive and permit passage of a portion of a wave and thus reduce the water displacement and buoyancy of the portion of the body provided with the vent or vents from what they would be with the full volume of the body without the vent or vents.

References Cited UNITED STATES PATENTS 2/ 1923 Gadomski 114-125 11/ 1949 Houghtaling 1l4--43.5 

1. A FLOATING BODY HAVING VOLUME AND WEIGHT, DISPLACING WATER ON WHICH IT IS FLOATING, SAID BODY PROVIDED WITH ONE OR MORE VENTS EACH IN THE FORM OF A STRAIGHT LONGITUDINAL PASSAGE OPEN AT ITS OPPOSITE ENDS, BOTH ENDS OF ALL OF SAID VENTS BEING DISPOSED ON THE EXTERNAL SURFACE OF SAID BODY ABOVE THE NORMAL WATER LEVEL AND ONE OF SAID ENDS OF EACH VENT DISPOSED ADJACENT SAID WATER LEVEL WHEN THE WATER IS CALM, EACH OF SAID VENTS LOCATED SO AS TO EXTEND LONGITUDINALLY OF THE BODY SOLELY IN AN OUTWARD DIRECTION AWAY FROM ITS CENTER OF GRAVITY AND ADAPTED TO RECEIVE AND PERMIT PASSAGE OF A PORTION OF A WAVE MOVING FROM FORE TO AFT AND THUS REDUCE THE WATER DISPLACEMENT AND BUOYANCY OF THE PORTION OF THE BODY PROVIDED WITH THE VENT OR VENTS FROM WHAT THEY WOULD BE WITH THE FULL VOLUME OF THE BODY WITHOUT THE VENT OR VENTS. 